Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
Generally, an image reading apparatus reads a document as follows. The image reading apparatus scans the document with light source, condenses the reflected light to a photoelectric conversion element such as a Charge Coupled Device (CCD) image sensor, and obtains an image signal corresponding to the document image. Then, an A/D convertor in an Analog Front End (AFE) performs A/D conversion on the image signal to obtain the document image data. This type of image reading apparatus employs a Cold Cathode Fluorescent Lamp (CCFL) as a light source. However, since the CCFL takes time for stabilizing luminance, the CCFL is always lit to improve a response speed. Consequently, there is a problem of causing quick deterioration. In view of this, recently, a light emitting diode (LED) is employed as a light source instead of the CCFL. The LED features low-price, long life, quick response speed, and long stabilization period. Accordingly, the LED features functionality sufficient for usual reading of documents.